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Learn the difference between blood clots that occur in the veins and clots which occur in arteries. Understand why certain medications are used for clots in the arteries while others are used for clots in the veins.

There are differences between clots which occur in the arteries and clots which occur in veins.

Differences between Arterial and Venous Clots

Arteries are the blood vessels through which the blood flows from the heart into the periphery: into the brain, the internal organs, the legs and the arms.

A clot in an artery leads to stroke, TIA (mini-stroke), heart attack, or peripheral arterial clot and gangrene (painful, cold, and pale digits or a whole extremity, later turning black).

Arterial Clot
Vein Clot Veins are the blood vessels that carry blood back to the heart.

A clot in the deep veins of legs, arms, abdomen or around the brain is called deep vein thrombosis (also called DVT for short).

If a piece of clot from a leg or arm DVT breaks off it can travel into the lung, causing a pulmonary embolism (PE).

What are blood clots made of?

Blood clots are made up of little particles called platelets and a meshwork of protein strands, called fibrin. Clots in arteries have a different composition than clots in veins.

Clots in arteries are mostly made up of platelets (figure 3).      Clots in veins mostly made up of fibrin.  (figure 4)

Clot Composition


Platelets are made slick and prevented from sticking together to form a clot by aspirin, Plavix®, Aggrenox®, Ibuprofen and a whole variety of so-called NSAIDs (non-steroidal anti-inflammatory drugs). Since platelets are the ones that mostly cause the clots in arteries, aspirin and these drugs are good to prevent clots in arteries.

Since platelets do not play much of a role in the clots in veins, aspirin is not very (if at all) useful to prevent clots in veins, such as DVT and PE. Heparin and warfarin ( Coumadin® ) are good in preventing fibrin from forming. They are, therefore, very effective drugs in preventing blood clots in veins from forming. Since fibrin also plays some role in clot formation in arteries, heparin and warfarin are also useful drugs in preventing artery clots. However, they cause more bleeding than aspirin and are, therefore, not the first choice in preventing artery clots.

 Clot Medications

Graphic designs above by Jeff Harrison, Stephan Moll®

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